Pruning Hydrangeas

Q: Please advise on the best time to prune hydrangeas.

A: Hydrangeas require differing pruning times; therefore, it is critical to know which type you have before you prune. In addition to using the techniques explained below, always remove any winter-damaged branches in early spring.

The climbing hydrangea (Hydrangea anomala ssp. petiolaris) grows to 50 to 60 feet and only requires pruning to keep it within its boundaries. Prune in early March.

The smooth hydrangea (Hydrangea arborescens) flowers on new wood and should be pruned down hard to 1 foot in early March. This species propagates itself by sending up many ground-level suckers, which may also be cut out. Failure to prune regularly results in a top-heavy shrub that flops to the ground by midseason.

The bigleaf hydrangea (Hydrangea macrophylla) flowers on old wood and should be pruned shortly after it flowers. Gardeners should not wait too late into fall before pruning because late-season pruning can stimulate tender new growth that might be killed during winter.

The panicle hydrangea (Hydrangea paniculata) and its cultivars also flower on new wood but don't require the drastic pruning of the smooth hydrangea. They will look best if one-third of the old growth is pruned back in late winter. If unpruned, these cultivars can reach 20 feet, which may be too large for certain landscapes.

The oakleaf hydrangea (Hydrangea quercifolia) flowers on old wood also but is often left unpruned since its spreading habit is quite attractive. The huge, 12-inch flowers are quite ornamental and will lend a late-season interest to the autumn garden. If the terminal buds of this type are killed off during winter, the plant will not flower.